One example of such oil immersed solenoid is shown in FIG. 9. The oil immersed solenoid is used to control the oil pressure and flow rate of operating oil flowing in a valve device (not shown) that is, for example, an oil-pressure device. To be specific, in an oil immersed solenoid 1, when a command electric signal (exciting current) is transmitted to an exciting coil 2, pulling force (pulling force in a left direction in FIG. 9) corresponding to the magnitude of the command electric signal is generated at a fixed magnetic pole portion 3, and the fixed magnetic pole portion 3 can pull a movable core 4 by the pulling force. When the movable core 4 is pulled, a rod 5 provided at the movable core 4 presses, for example, a spool of the valve device (not shown) in the left direction in FIG. 9. This pressing force balances push-back force (push-back force in a right direction in FIG. 9) based on, for example, spring force or pilot pressure applied to the spool. The spool stops at a position where the pressing force and the push-back force are balanced. With this, the oil pressure and flow rate of the operating oil flowing in the valve device can be controlled so as to be proportional to the command electric signal.
However, if air and air bubbles exist in the oil, such as the operating oil, in the space 6 of the oil immersed solenoid 1, this may cause an irregular change in acceleration of the movable core 4, and chattering of the movable core 4 may occur.
Here, in order to remove the air and the air bubbles in the space 6 of the solenoid 1, an adjusting screw 9 is provided to threadedly engage with a rear metal member 8 sealing a rear opening 7 of the solenoid 1 shown in FIG. 9, and the air and the air bubbles in the solenoid 1 can be removed by loosening or removing the adjusting screw 9.
Moreover, even among the standardized oil immersed solenoids 1 shown in FIG. 9, each solenoid 1 has its own characteristics, and the sizes of the parts constituting the solenoids 1 vary. Therefore, even if the same command electric signal is transmitted, the pulling force of the fixed magnetic pole portion 3 varies, so that the pressure and flow rate of the operating oil in the valve device vary. Therefore, the variations of each of the pressure and flow rate need to be kept within an allowable range, which is a difficult problem. This is because the allowable range of the variations is generally narrow, and there are certain limitations on reducing the variations in size of each part.
Here, as shown in FIG. 9, an adjusting spring 10 is provided. The adjusting spring 10 is configured to bias the movable core 4 in the same direction as the pulling force of the fixed magnetic pole portion 3, and the biasing force can be adjusted by the adjusting screw 9.
With this, when a predetermined command electric signal is transmitted to the solenoid 1, the biasing force of the adjusting spring 10 can be adjusted by the adjusting screw 9 in advance or accordingly such that each of the predetermined pressure and flow rate is proportional to the command electric signal and falls within a predetermined allowable range.
Another example of the oil immersed solenoid 1 is disclosed in Japanese Laid-Open Patent Application Publication No. 2006-140417 (see PTL 1 for example).